The tumor we are using in this study is the Sarcoma I (Sa I) tumor which is maintained in the ascites form in syngeneic A/J (H-2a) mice by weekly serial transplantation. This tumor is also maintained in tissue culture by our laboratory. Injections of 10 to the third power-10 to the fourth power Sa I cells kills 60-80% of A/J mice in 30-50 days. Immunity to this challenge dose can be induced in A/J mice by pretreatment with irradiated Sa I cells. We have recently demonstrated that splenectomy performed three weeks prior to tumor challenge reduces the mortality from 60-80% to 20-40%. At the time of tumor challenge the effect of splenectomy can be reversed by adoptive transfer of spleen cells that do not adhere to Sephadex G-10. These findings indicate that the spleen contains lymphocytes which regulate the immune response against syngeneic tumors. The specific aims of this research project are to: 1. identify the spleen cell subpopulation of lymphocytes involved in the regulation of the immune response against syngeneic tumors; (2) produce continuous tissue culture cell lines of T-lymphocytes with cytotoxic activities against the Sa I tumor; and 3. to extend these studies to other tumor-host systems. The overall goal of this research project is to have a better understanding of the immunological reactions between the host and the tumor in terms of the cells (B cells, T cell, null cells, and macrophages) involved in the immunological rejection and enhancement of tumor growth.